When a vehicle is driven with one or more windows and/or the sunroof open, the vehicle may exhibit a wind throb condition. Wind throb is a low frequency pressure oscillation that can be described as “helicopter” noise. Generally wind throb is associated with frequencies between 12 and 18 hertz. In the event pressure oscillations are high enough, the occupants of the vehicle will become dissatisfied and annoyed then close the windows and/or sunroof. Open window throb is caused by the coupling of the unsteady flow of air over the opening with the cabin acoustic resonance mode. Wind throb has become more common on vehicles over the last 10 years as a result of improved vehicle aerodynamics and tighter body sealing. Thus, the wind throb condition has become more prevalent and a need exists for an improved solution.
U.S. Patent Application Publication No. 2009/0088065, assigned to Ford Global Technologies, LLC, discloses a prior art air extractor that is fitted behind the license plate or other rear facing surface of the vehicle where it is adapted to relieve air pressure changes in the interior of the vehicle and control wind throb. The device consists of an air extractor opening that may be opened and closed by means of a closure member. More specifically, the opening is normally closed to seal the interior of the vehicle but is opened when wind throb conditions are sensed so as to allow the flow of air from the interior of the vehicle to alleviate wind throb.
While useful for its intended purpose, the air extractor disclosed in 2009/0088065 is not specifically tuned to the wind throb frequencies characteristic of the vehicle in which it is mounted and, therefore, it cannot provide the most efficient and effective relief of the wind throb condition.
This document relates to an air extractor with multiple flaps that are tuned to resonate at a specific frequency or frequencies equal to the expected peek throb frequencies for the vehicle in which the air extractor is mounted. The flaps are allowed to pivot inwardly toward the passenger compartment of the vehicle and outwardly toward the exterior surface of the vehicle so as to provide enough damping to reduce throb amplitudes/peek throb levels characteristic of the vehicle in which the extractor is mounted.